In recent years there has been a substantial increase in the use of percutaneous transluminal angioplasty for the treatment of vascular stenoses and, particularly, stenoses of the coronary arteries. The use of balloon dilatation catheters for such angioplasty procedures may provide for many patients an effective alternative to coronary artery bypass surgery.
In a typical coronary angioplasty procedure, a guide catheter is introduced into the patient's arterial system through the femoral artery and is advanced through the aorta and to the ostium of the coronary artery. Once the guide catheter is positioned with its tip intubated in the coronary ostium, a balloon dilatation catheter which typically will have been fitted with a small diameter guidewire, such as the steerable guidewire disclosed in U.S. Pat. No. 4,453,930, is advanced through the guide catheter to and into the coronary artery. Once the dilatation catheter and steerable guidewire are located in the coronary arterial tree, the catheter is positioned by manipulations of the catheter and the guidewire in which the distal tip of the guidewire is selectively steered through the branches and tortuous passages of the arterial anatomy and with dilatation catheter being advanced over the guidewire after the guidewire is positioned. When the balloon is positioned in the stenosis, it is inflated under pressure to effect the dilatation, thereby, forcably enlarging the narrowed lumen of the artery.
Among the desirable features of the dilatation catheter is that it should be highly flexible so that it can track easily along the guidewire through sharp bends and tortuous coronary arteries. If the catheter is too stiff, it will not track well and instead of following the natural contour of the artery and flexible guidewire, it will tend to straighten the artery which causes it to press against the arterial walls as well as the guidewire which, in turn, presents difficulty in manipulating and positioning the guidewire and catheter. Another difficulty encountered with balloon dilatation catheters is that the presence of the catheter in the artery presents an obstruction to blood flow in the artery. Where the angioplasty procedure is performed in arteries that are already suffering from narrowing stenoses, the presence of the catheter during the angioplasty procedure itself presents an obstruction and somewhat of an increased risk of ischemia in distal portions of the artery. It is among the general objects of the invention to provide an improved dilatation catheter that displays superior trackability and also minimizes the degree of obstruction within the artery.
The angioplasty procedure typically includes the periodic injection of radiopaque dyes into the coronary arterial tree to enable the physician to observe, fluoroscopically, the conditions of the coronary anatomy during the procedure as well as to visualize the anatomy to help in positioning the dilatation catheter. It also is among the common procedures to make measurements of the blood pressure both proximally and distally of the stenosis to compare the pressure gradient in the artery before the dilatation with the pressure gradient after dilatation. Ideally, the dilatation procedure enlarges the arterial obstruction thereby reducing the pressure gradient along that region. The observation of a reduced pressure gradient signifies that the dilatation procedure is accomplishing its objective and is an important feature to be monitored by the physician. Typically, the guide catheter, the tip of which is in communication with the cornary ostium, is used to inject dye into the coronary arterial tree as well as to make pressure measurements on the proximal side of the stenosis. In order to obtain enhanced dye injections and pressure measurements, it is desirable that the cross-sectional flow area through the guide catheter be as large as possible. However, it also is desirable to maintain a reduced diameter for the guide catheter so that it will be more easily inserted into the patient and so that the distal end of the guide catheter may be more securely intubated into the coronary ostium. It is among the general objects of the invention to provide a modified dilatation cathether which achieves these objectives.
Thus, it is among the general objects of the invention to provide a novel dilatation catheter construction which displays superior tracking and a low profile for the balloon as well as for the distal segment of the catheter and which provides other significant advantages over prior diliation catheters.